CN105537695A - Coarse-pitch external thread layered turning process - Google Patents

Abstract

The invention relates to an external thread turning process, in particular to a coarse-pitch external thread layered turning process. The process aims at solving the problem that by means of existing thread turning methods, because the requirements for massive removal and high-precision machining of coarse-pitch external threads can not be met, thread surface machining principle errors and cutter marks exist in coarse-pitch external thread turning, the problem that because of the overlarge cutting load, cutter abrasion is quick, and the problem that because of staggered threads and an excessively large number of layered cutting times caused by cutter starting point error accumulation, the machining efficiency is low is solved. The process includes the process of conducting rough machining by removing thread rough machining allowance through multiple cutting edges in a radial continuous multi-time feed layered cutting mode and a left-right axial multi-time layered cutting mode, and the process of conducting semi fine machining and fine machining in a layered cutting mode by feeding the left cutting edge and the right cutting edge alternately multiple times in the axial direction. The requirements for the machining precision and the machining surface quality of external threads are met, obtained left and right threaded faces are free of cutter marks, the problem that threads are meshed in disorder is solved, and the requirement for efficiently turning coarse-pitch external threads in a high-quality mode is met.

Description

Coarse pitch external screw thread layering turning technique

Technical field

The present invention relates to a kind of external threading technique, be specifically related to coarse pitch external screw thread layering turning technique, belong to turning process technical field.

Background technology

The external screw thread that pitch is greater than 4mm is defined as coarse pitch external screw thread, and this type of part, as large pressing machine adjustment assembly screw rod, controls the positional precision between bolster, has material impact to quiet, the dynamic accuracy of forcing press complete machine.Coarse pitch external screw thread tooth form groove width and dark, pitch and axial length large, belong to odd-pitch screw, allowance is large, pitch and profile accuracy and thread surface quality requirement high.

The externally threaded processing method of existing coarse pitch mainly contains milling, grinding, turning and processing and forming, processing and forming load is large and be difficult to the processing request meeting different size screw thread, and working (machining) efficiency is lower, during Milling Process coarse pitch external screw thread, interrupted cut can aggravate the vibration in screw rod processing, and limits by cutter life, the screw thread that improper processing axial length is long, is only applicable to processing short thread, when adopting method for grinding processing coarse pitch external screw thread, high accuracy of thread and surface quality can be obtained, but its blank needs the precision level first adopting other processes to reach certain, and the method requires higher when processing diameter and the larger threaded male component of axial dimension to technological equipment, adopt method for turning processing coarse pitch external screw thread, crudy and working (machining) efficiency can be ensured, be easy to again design fixture system, but existing thread turning processing method is mainly used in the screw thread process of middle-size and small-size pitch, the externally threaded large surplus of coarse pitch cannot be reached remove and high accuracy processing request, coarse pitch external threading processing in exist thread surface processing original reason error and connect tool marks, the excessive tool wear caused of chip-load is too fast, play the screw thread disorderly button that the accumulation of cutter point tolerance produces, the problems such as working (machining) efficiency reduction are too much caused with layered cutting number of times, how to design feed mode, how to control the load in working angles, chip removal, to ensure the requirement of machining accuracy and crudy and to improve stock-removing efficiency, become large pressing machine large-lead screw and process key issue urgently to be resolved hurrily.

Summary of the invention

The object of the invention is the screw thread process being mainly used in middle-size and small-size pitch in order to solve prior art thread turning processing method, the externally threaded large surplus of coarse pitch cannot be reached remove and high accuracy processing request, there is the original reason error of thread surface processing during coarse pitch external threading is processed and connect tool marks, the excessive tool wear caused of chip-load is too fast, and the random button of screw thread and the layered cutting number of times that play cutter point tolerance accumulation generation too much cause the problems such as working (machining) efficiency reduction.

Technical scheme of the present invention is: coarse pitch external screw thread layering turning technique, and described turning process comprises the following steps:

Step one, roughing process: adopt the mode of multiple-cutting-edge radially continuous several times feed layered cutting to remove external screw thread roughing surplus, make externally threaded radial dimension reach requirement; Adopt the mode of left and right sword continuous several times feed vertically layered cutting, remove and connect tool marks when radially layered cuts, form external screw thread basic profile structure and left and right flank, to reduce screw thread roughing geometric error and following process surplus;

Step 2, semifinishing process: adopt left cutting edge and right cutting edge to replace vertically repeatedly feed layered cutting mode and remove allowance, to reach externally threaded machining accuracy and machined surface quality requirement;

Step 3, finishing passes: adopt left cutting edge and right cutting edge to replace vertically repeatedly feed layered cutting mode and remove allowance.

Step 2 and the axial repeatedly feed layered cutting method described in step 3 solve the problem that in the cutting of multiple-cutting-edge radially layered, two-edged is interfered mutually, make to be independent of each other between two-edged in cutting, therefore, the method is adopted can to meet machining accuracy and the machined surface quality requirement of steep-pitch thread.

Radial cutting mode described in step one adopts 3-edge surgical knife tool to cut,, each time during radial feed, three cutting edges of cutter all participate in cutting, its cutting lay area is all greater than the cutting lay area of a front radial feed, its cutting lay area and each radial cutting-in a _piwith the left and right cusp angle ε ' of cutter _r1, ε ' _r2relevant;

Aspect face S is cut when i-th time three sword radially layereds cut _ifor: S _i=S ₁+ S ₂+ S ₃;

In formula, S ₁, S ₂and S ₃be respectively the cutting lay area of 3-edge surgical knife tool, determine especially by following formula:

$S_1=h_{D1}\·b_{D1}=(a_{pi}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}1}}^{\′}\·{{\mathrm{cos\ϵ}}_{\mathrm{\γ}1}}^{\′})\·(\underset{k=1}{\overset{i-1}{\Σ}}{a}_{Pk}/{{\mathrm{cos\ϵ}}_{\mathrm{\γ}1}}^{\′})=a_{Pi}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}1}}^{\′}\·\left(\underset{k=1}{\overset{i-1}{\Σ}}{a}_{Pk}\right);$

$S_2=h_{D2}\·b_{D2}=(a_{pi}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}2}}^{\′}\·{{\mathrm{cos\ϵ}}_{\mathrm{\γ}1}}^{\′})\·(\underset{k=1}{\overset{i-1}{\Σ}}{a}_{Pk}/{{\mathrm{cos\ϵ}}_{\mathrm{\γ}2}}^{\′})=a_{Pi}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}2}}^{\′}\·\left(\underset{k=1}{\overset{i-1}{\Σ}}{a}_{Pk}\right);$

$S_3=\frac{1}{2}\·a_{pi}\·(2b+h_{D31}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}1}}^{\′}+h_{D32}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}2}}^{\′});$

Wherein, ε _r1' and ε _r2' being respectively the half of thread angle of cutter left and right sword, b is cutter head width, and h is cutting tool insert total height, a _pfor total radial cutting degree of depth, a _pibe the cutting depth of i-th radial cutting, h _d1the cutting layer thickness in left-hand thread face during for cutting, h _d2the cutting layer thickness in right-hand thread face during for cutting, h _d3the cutting layer thickness of flank at the bottom of tooth during for cutting, b _d1the cutting lay width in left-hand thread face during for cutting, b _d2the cutting lay width in right-hand thread face during for cutting.

Step one is carried out in roughing process, and cutter axial feed velocity and cutting speed are mutually vertical.

In step 2 and step 3 in axial layered cutting process, during jth time axial layered cutting, cutting to left and right sword cuts aspect S _jfor;

S _j＝z _j·a _P；

Wherein, z _jfor allowance axial when jth secondary clearing cuts, the radial cutting degree of depth a of each axial feed _pbe the form of thread degree of depth.

Described turning process comprises cooling procedure, and when carrying out fine finishining described in step 3, last twice feed adopts aqueous emulsion to cool, and other working angles adopt lubricating oil to cool.

In described turning process, machine spindle speed meets: machine spindle speed in machine spindle speed > finishing passes in machine spindle speed > semifinishing process in roughing process.

The present invention compared with prior art has following effect: the method adopts radially layered to cut and axial stratification cutting process, carry out the roughing of coarse pitch external screw thread, utilize cutter cutting to left and right sword and top sword, by the mode of radially continuous several times feed layered cutting, cut number of times with minimum radially layered and remove roughing surplus, reach the radial dimension requirement of screw thread, and cut with the axial stratification of minimum number, form external screw thread basic profile structure and left and right flank, to reduce screw thread roughing geometric error, not only significantly improve the externally threaded roughing working (machining) efficiency of coarse pitch, and decrease following process surplus and axial stratification cutting number of times,

Adopt axial stratification cutting process, left cutting edge and right cutting edge is utilized to carry out the semifinishing of coarse pitch external screw thread and fine finishining respectively, to control chip-load, avoid cutter to produce the problems such as distortion and rapid wear because load is excessive, significantly improve accuracy of screw machining and machined surface quality; This method for designing is with minimum layered cutting number of times, reach externally threaded machining accuracy and machined surface quality requirement, the left and right flank obtained is without connecing tool marks, pitch error controls within the scope of-0.02mm ~ 0.02mm, eliminate the random button problem of screw thread, externally threaded efficient, the high-quality turnery processing requirement of coarse pitch can be met.

Accompanying drawing explanation

Fig. 1 radially layered cutting way and parameter of cutting layer schematic diagram thereof, Fig. 1 (a) is radial cutting schematic diagram; Fig. 1 (b) is that i-th radial feed parameter of cutting layer characterizes schematic diagram;

Fig. 2 axial stratification cutting way and parameter of cutting layer schematic diagram thereof, Fig. 2 (a) is axial stratification cutting schematic diagram; Fig. 2 (b) is jth time axial feed parameter of cutting layer sign schematic diagram;

Fig. 3 turning steep-pitch thread process chart;

The trapezoidal screw thread pitch error measurement result schematic diagram of Fig. 4 embodiment of the present invention, Fig. 4 (a) is left-hand thread error result schematic diagram, and Fig. 4 (b) is right-hand thread error result schematic diagram;

The left and right flank milled surface topography contrast schematic diagram of Fig. 5 embodiment of the present invention, Fig. 5 (a) for left-hand thread finished surface contour curve figure, Fig. 5 (b) be right-hand thread face finished surface contour curve figure.

In way, n is workpiece rotational frequency, V _ffor cutter axial feed velocity, κ _rfor cutter tool cutting edge angle, κ _r＇ is cutter auxiliary angle, ε _r1' and ε _r2' being respectively the half of thread angle of cutter left and right sword, b is cutter head width, and h is cutting tool insert total height; D is the external diameter of test specimen, d ₂for the central diameter of test specimen, d ₁for the path of test specimen; a _pfor total radial cutting-in, a _pibe the cutting depth of i-th radial cutting, h _d1the cutting layer thickness in left-hand thread face during for cutting, h _d2the cutting layer thickness in right-hand thread face during for cutting, h _d3the cutting layer thickness of flank at the bottom of tooth during for cutting, b _d1the cutting lay width in left-hand thread face during for cutting, b _d2the cutting lay width in right-hand thread face during for cutting; P is test specimen pitch, and B is that test specimen tooth is wide, and H is that test specimen tooth is high, R ₁, R ₂be respectively the tooth form radius of test specimen left and right side, r ₁, r ₂be respectively the crest radius of cutter left and right sword; Z _lifor left sword cuts single process surplus, Z _rifor right sword cuts single process surplus (wherein i=1,2 ... w, j=1,2 ... m), h _d1cutting layer thickness during sword turning left for cutter, b _d1cutting lay width during sword turning left for cutter, h _drcutting layer thickness during sword turning right for cutter, b _drcutting lay width during sword turning right for cutter.

Detailed description of the invention

Accompanying drawings the specific embodiment of the present invention, the coarse pitch external screw thread layering turning technique of present embodiment, the 35CrMo trapezoidal screw of turning pitch 16mm, external diameter 120mm, specifically comprises the following steps:

Step one, roughing process: adopt the mode of radially continuous several times feed layered cutting to remove external screw thread roughing surplus, make externally threaded radial dimension reach requirement, specifically as shown in Figure 1; Adopt the mode of left and right sword continuous several times feed vertically layered cutting to remove and connect tool marks when radially layered cuts, form external screw thread basic profile structure and left and right flank, reduce screw thread roughing geometric error and following process surplus, specifically as shown in Figure 2; Roughing technique, by controlling the single radial cutting degree of depth and the axial allowance of single, with effective control load, avoids cutter that significantly distortion occurs because load is excessive;

There is the problem that in working angles, two-edged is interfered in which, in cutting, in two cutting edges, any sword changes all can affect tooth form, wherein, if there is a sword to reach the limit of wear, then can thoroughly cause tooth form to lose efficacy, the method be high to the angle requirement between two cutting edges, and once after process finishing, tooth form precision and immutable.Therefore, the method is only suitable for being applied in steep-pitch thread roughing, for meeting the requirements of cutting depth;

Described radial cutting mode adopts 3-edge surgical knife tool to cut, the cutting lay area S of 3-edge surgical knife tool ₁, S ₂and S ₃determined by following formula:

$S_1=h_{D1}\·b_{D1}=(a_{pi}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}1}}^{\′}\·{{\mathrm{cos\ϵ}}_{\mathrm{\γ}1}}^{\′})\·(\underset{k=1}{\overset{i-1}{\Σ}}{a}_{Pk}/{{\mathrm{cos\ϵ}}_{\mathrm{\γ}1}}^{\′})=a_{Pi}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}1}}^{\′}\·\left(\underset{k=1}{\overset{i-1}{\Σ}}{a}_{Pk}\right);$

$S_2=h_{D2}\·b_{D2}=(a_{pi}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}2}}^{\′}\·{{\mathrm{cos\ϵ}}_{\mathrm{\γ}1}}^{\′})\·(\underset{k=1}{\overset{i-1}{\Σ}}{a}_{Pk}/{{\mathrm{cos\ϵ}}_{\mathrm{\γ}2}}^{\′})=a_{Pi}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}2}}^{\′}\·\left(\underset{k=1}{\overset{i-1}{\Σ}}{a}_{Pk}\right);$

$S_3=\frac{1}{2}\·a_{pi}\·(2b+h_{D31}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}1}}^{\′}+h_{D32}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}2}}^{\′});$

Aspect face S is cut when i-th time three sword radially layereds cut _ifor: S _i=S ₁+ S ₂+ S ₃;

Wherein, ε _r1' and ε _r2' being respectively the half of thread angle of cutter left and right sword, b is cutter head width, and h is cutting tool insert total height, a _pfor total radial cutting degree of depth, a _pibe the cutting depth of i-th radial cutting, h _d1the cutting layer thickness in left-hand thread face during for cutting, h _d2the cutting layer thickness in right-hand thread face during for cutting, h _d3the cutting layer thickness of flank at the bottom of tooth during for cutting, b _d1the cutting lay width in left-hand thread face during for cutting, b _d2the cutting lay width in right-hand thread face during for cutting.

Cutter axial feed velocity and cutting speed are mutually vertical.

Step 2, semifinishing process: adopt left cutting edge and right cutting edge to replace vertically repeatedly feed layered cutting mode and remove allowance;

Step 3, finishing passes: adopt left cutting edge and right cutting edge to replace vertically repeatedly feed layered cutting mode and remove allowance.

In step 2 and step 3 in axial layered cutting process, when jth secondary clearing cuts, cutting to left and right sword cutting lay area S _jfor:

S _j＝z _j·a _P；

Wherein, z _jfor allowance axial when jth secondary clearing cuts, a _pfor radial cutting-in.

After fine finishining, the allowance of left and right sides is 0.8mm;

Present embodiment is thick, partly essence and the finishing machine speed of mainshaft are respectively 25r/min, 16r/min and 10r/min;

In the roughing of present embodiment, radial cutting experiences 22 feeds altogether, and axial stratification cuts and experiences 55 feeds altogether;

35 axial layered cuttings are experienced in the semifinishing of present embodiment altogether, and 26 axial layered cuttings are experienced in fine finishining altogether;

Last twice feed of left and right flank fine finishining of present embodiment adopts aqueous emulsion to cool, and other working angles adopt lubricating oil to cool;

The shown trapezoidal externally threaded fine finishining scheme of turning pitch 16mm is as shown in table 1:

Table 1 fine finishining scheme:

Coarse pitch external threading has three kinds of feed modes usually, and namely radial feed, sideway feed and left and right replace feeding; Existing method for turning adopts above-mentioned three kinds of feed modes to carry out adding man-hour, for Simplified flowsheet, usually in roughing, single feed mode is adopted, in semifinishing and fine finishining, the surplus such as to adopt cut, feed number of times, feed order and the unreasonable chip-load that causes of allowance design frequently change, the flank machining accuracy that tool displacement, distortion and wearing and tearing cause and machined surface quality decline, not only seriously restrict the lifting of coarse pitch external screw thread working (machining) efficiency, even cause large pressing machine screw rod to scrap.

At present, the main nose part of cutter that adopts of turning coarse pitch external screw thread processing is divided into conduct to successively cutting, by controlling the site error of point of a knife, control the formation of thread surface, this cutting way reduces NC Machining Program difficulty, but due to flank be point of a knife close approximation formed, there is original reason error, thread surface has and obviously connects tool marks, and each allowance cut is little.For this reason, Circular Nose Cutting Edge cutter is adopted to carry out turning, machining accuracy and machined surface quality are guaranteed substantially, but because each feed adopts little surplus to cut, too much cutting number of times not only increases the cutting time, and extends cutting stroke, Tool in Cutting sword effect of attrition screw thread surface precision, the screw thread playing cutter point tolerance accumulation generation of each cutting disorderly detains problem, directly has influence on the pitch precision of screw rod.

The present invention devises the radial and axial layered cutting of turning coarse pitch external screw thread two kinds of tool feeding methods, utilizes cutting to left and right tooth shape to become left and right flank, eliminates the original reason error of point of a knife close approximation generation and connects tool marks; According to each feed cutting lay area, determine the allowance of single feed, effectively control chip-load; In roughing, first radially layered cutting process is adopted to remove external screw thread roughing surplus with minimum layered cutting number of times, reach externally threaded radial dimension requirement, again with the axial stratification cutting process of minimum number, form the left and right flank of degree of precision, to reduce follow-up semifinishing and accurately machined cutting number of times, obtain high stock-removing efficiency; In semifinishing and fine finishining, adopt axial stratification cutting process, solve the problem that in the cutting of multiple-cutting-edge radially layered, two-edged is interfered mutually, utilize left cutting edge and right cutting edge to carry out layered cutting respectively, to improve accuracy of screw machining and machined surface quality; Adopt the process program that this method for designing obtains, effectively can ensure the externally threaded machining accuracy of coarse pitch and machined surface quality.

The pitch error of the screw rod left and right flank of present embodiment turning along workpiece axial distribution as shown in Figure 4; In figure, the flank of the left cutting edge processing of cutter is left-hand thread face, and the flank of the right cutting edge processing of cutter is right-hand thread face.As shown in Figure 4, although the pitch error distribution of left and right flank is obviously different, its error all changes between-0.02mm ~ 0.02mm, meets trapezoidal screw requirement on machining accuracy;

Present embodiment obtains the machined surface pattern of screw rod left and right flank as shown in Figure 5:

Utilize and processed roughness concentration curve, extract and process roughness value, the quality of quantitative analysis workpiece left and right flank machined surface quality, as shown in table 2:

Table 2 machined surface roughness value

In table 2, R _afor surface profile arithmetic average deviation, R _smfor profile cell-average width, S _kfor profile elevations h mal-distribution parameter; Wherein, standard deviation reflection is the dispersion degree of data;

As can be seen from Fig. 5 and table 2, although the machined surface quality in right-hand thread face is significantly better than left-hand thread face, its surface roughness average is all less than 3.2 μm, meets processing request.

Claims (6)

1. coarse pitch external screw thread layering turning technique, is characterized in that: described turning process comprises the following steps:

Step one, roughing process: adopt the mode of multiple-cutting-edge radially continuous several times feed layered cutting to remove external screw thread roughing surplus, externally threaded radial dimension is made to reach requirement, adopt the mode of left and right sword continuous several times feed vertically layered cutting of minimum number to remove and connect tool marks when radially layered cuts, form external screw thread basic profile structure and left and right flank, to reduce screw thread roughing aggregate error and following process surplus;

Step 2, semifinishing process: adopt left cutting edge and right cutting edge to replace vertically repeatedly feed layered cutting mode and remove allowance;

Step 3, finishing passes: adopt left cutting edge and right cutting edge to replace vertically repeatedly feed layered cutting mode and remove allowance.

2. coarse pitch external screw thread layering turning technique according to claim 1, is characterized in that: radial cutting mode described in step one adopts 3-edge surgical knife tool to cut, the cutting lay area S of 3-edge surgical knife tool ₁, S ₂and S ₃determined by following formula:

$S_1=h_{D1}\·b_{D1}=(a_{pi}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}1}}^{\′}\·{{\mathrm{cos\ϵ}}_{\mathrm{\γ}1}}^{\′})\·(\underset{k=1}{\overset{i-1}{\Σ}}{a}_{Pk}/{{\mathrm{cos\ϵ}}_{\mathrm{\γ}1}}^{\′})=a_{Pi}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}1}}^{\′}\·\left(\underset{k=1}{\overset{i-1}{\Σ}}{a}_{Pk}\right);$

$S_2=h_{D2}\·b_{D2}=(a_{pi}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}2}}^{\′}\·{{\mathrm{cos\ϵ}}_{\mathrm{\γ}1}}^{\′})\·(\underset{k=1}{\overset{i-1}{\Σ}}{a}_{Pk}/{{\mathrm{cos\ϵ}}_{\mathrm{\γ}2}}^{\′})=a_{Pi}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}2}}^{\′}\·\left(\underset{k=1}{\overset{i-1}{\Σ}}{a}_{Pk}\right);$

$S_3=\frac{1}{2}\·a_{\mathrm{\ρ}i}\·(2b+h_{D31}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}1}}^{\′}+h_{D32}\·{{\mathrm{sin\ϵ}}_{\mathrm{\γ}2}}^{\′});$

Aspect face S is cut when i-th time three sword radially layereds cut _ifor: S _i=S ₁+ S ₂+ S ₃;

Wherein, ε _r1' and ε _r2' being respectively the half of thread angle of cutter left and right sword, b is cutter head width, and h is cutting tool insert total height, a _pfor total radial cutting degree of depth, a _pibe the cutting depth of i-th radial cutting, h _dlthe cutting layer thickness in left-hand thread face during for cutting, h _d2the cutting layer thickness in right-hand thread face during for cutting, h _d3the cutting layer thickness of flank at the bottom of tooth during for cutting, b _d1the cutting lay width in left-hand thread face during for cutting, b _d2the cutting lay width in right-hand thread face during for cutting.

3. coarse pitch external screw thread layering turning technique according to claim 1, is characterized in that: step one is carried out in roughing process, cutter axial feed velocity and cutting speed form right angle coordinate system.

4. coarse pitch external screw thread layering turning technique according to claim 1, is characterized in that: in step 2 and step 3 in axial layered cutting process, when jth secondary clearing cuts, cutting to left and right sword cutting lay area S _jfor:

S _j＝z _j·a _P；

Wherein, z _jfor allowance axial when jth secondary clearing cuts, a _pfor radial cutting-in.

5. coarse pitch external screw thread layering turning technique according to claim 1, it is characterized in that: described turning process comprises cooling procedure, when carrying out fine finishining described in step 3, last twice feed adopts aqueous emulsion to cool, and other working angles adopt lubricating oil to cool.

6. coarse pitch external screw thread layering turning technique according to claim 1, is characterized in that: in described turning process, machine spindle speed meets: machine spindle speed in machine spindle speed > finishing passes in machine spindle speed > semifinishing process in roughing process.